This invention relates to canisters for computer output microfilm printers and, more particularly, to a computer output microfilm canister arranged to compute and display the length of film remaining in the canister and to provide appropriate signals to computer output microfilm recording systems.
In computer output microfilm ("COM") systems, light-tight replaceable canisters are designed to be removably installed in the system to supply film to a camera on demand and to provide appropriate signals to the system in accordance with the use-of the film in the canister to indicate the length of film remaining in the canister.
In some COM systems these signals are generated by spaced irregularities in a flange rim or disc which is rotated by withdrawal of film from a roll of film in the canister and, consequently, the signals are generated at a higher rate as the diameter of the roll of film decreases.
Laser COM recorders are capable of exposing several different types of microfilm in the same system and, if an operator removes an existing film supply canister containing one type of film and replaces its with a canister containing a different type of film, information stored in the system relating to the length of film remaining in the first canister is lost when that canister is replaced. In order to retain information regarding the length of film remaining in a canister thus removed before the film supply has been depleted, it is necessary for the COM system operator to record that information on the canister or on a film end extending from the canister.
Moreover, while disposable film canisters, which are designed for single use, contain information about the film such as the film type and film emulsion number printed on the canister, such canisters have the disadvantage of higher cost and produce environmental waste that must be disposed of properly. As a result, high volume COM service bureaus prefer to use reloadable film supply canisters, but unless the appropriate information about the film is marked on the canister each time it is loaded, the operator of the system has no way of knowing what type of film is being used.
U.S. Pat. No. 4,987,300 discloses a COM film canister having an optical-mechanical rotation sensing mechanism which produces an external light signal generated by rotation of a flange connected to a film roll within the canister. As film is withdrawn from the canister, these signals are transmitted to a computer in a COM system which computes the length of film remaining in the canister, taking into account the decreasing diameter of the film in the roll as it is used. If the canister is removed from the COM system, however, the remaining film length information is lost.
Similarly, U.S. Pat. Nos. 5,153,625; 5,247,323 and 5,389,992 disclose film canisters for use with COM systems in which rotation of a disk associated with a film roll contained within a canister generates signals which are sensed through the canister housing by an external detector in the COM system and those signals are used by the system to determine the length of film remaining based on the decreasing diameter of the film roll contained in the canister as the film is used. With this arrangement as well, information relating to the length of film remaining in a canister is lost if the canister is replaced temporarily with another film canister. For such canisters in which the film roll is partially used and the remaining film length is not recorded manually, the length of film remaining in the canister must be redetermined after the canister has been replaced in the system by withdrawing several feet of film to permit a calculation based on the detected rate of motion of the disk or flange associated with the film roll in the canister.